While we have to keep an eye on the old folk so they stay warm enough to avoid hypothermia, there is an upside for the rest of us feeling the cold.

Believe it or not, it will give your metabolism a boost. Shivering is good for you.

Shivering in the cold sparks biochemical reactions deep within the body that alter fat cells and bolster metabolism, much as ­exercise does, according to a ­fascinating series of new ­experiments. The findings reveal exercise and shivering are related, but in ways not suspected before.

Scientists enrolled 10 healthy men and women in three different test sessions.

In the first they exercised them to exhaustion on exercise bicycles. For the second, participants cycled for an hour at a leisurely pace, both of these sessions at 65F (18.3C).

On their third visit, volunteers lay in bed for 30 minutes as the lab temperature dropped down to a chilly 53F (11.6C). Monitors ­measured skin and muscle ­reactions while the volunteers shivered.

After each session, the scientists checked for changes in the volunteers’ white and brown fat.

Why? Well, brown fat burns calories. Babies have lots of it to keep them warm since they can’t shiver. ­Scientists always thought that adults lose their brown fat and shiver instead to stay warm.

Newer studies, however, have ­discovered that brown fat stores in people of all ages. But why do we continue to shiver if we have brown fat? Shouldn’t one or the other be sufficient for us to face the cold?

Exercise creates a lot of heat when working muscles burn fuel and generate energy. So does ­shivering, but shivering does more.

It ­stimulates the ­production of a hormone called irisin, which converts useless white fat into ­fuel-burning brown fat.

The US investigators ­demonstrated the power of ­shivering. For while the volunteers’ blood levels of an irisin marker rose after exercise, the markers were just as high after they had lain still in the cold for 30 minutes.

What seemed to matter wasn’t the amount of exertion but the simple contraction of muscles, which happens during shivering as well as cycling.

The theory is that shivering came first. Irisin originally was created by muscular contractions during shivering. ­Exercise increases irisin ­production not because it’s exercise, but because it’s ­basically an ­exaggerated form of shivering.

So next time you shiver and your teeth start to chatter, just remember while it may feel uncomfortable it’s ­actually doing you good.